1. Field of the Invention
The invention relates to novel compositions, and in particular, to tough impact resistant ABS polymers having a relatively narrow particle size range and process therefor.
2. Description of the Prior Art
In the last several years, numerous U.S. and foreign patents have issued involving latex suspension processes. None of these patents, which are described below suggests the unexpectedly excellent properties obtained by using small particle size spine in the latex-suspension processes. Small particle size spine, hereinafter referred to as "SPS spine" as used herein is meant to signify a spine prepared by conventional emulsion techniques, and consisting of rubber particles from about 0.02-0.14.mu. in diameter with at least 60% less than 0.07.mu. in diameter. A large particle size spine hereinafter referred to as "LPS spine" as used herein is meant to signify a spine prepared by conventional emulsion techniques, and consisting of rubber particles from about 0.05-1.00.mu. in diameter.
British Patent No. 1,299,268 discloses a process wherein an 80/20 spine/resin graft latex is added to styrene and acrylonitrile monomers, the latex is coagulated and the water phase is separated. The resulting cement of monomers soaked up in the graft is polymerized in bulk. The reference discloses that polymerization may also be performed using suspension techniques.
In U.S. Pat. No. 3,751,526 there is described a process, involving the addition of a spine latex to monomers followed by coagulation and separation of the water phase. The polymerization is run in bulk. No disclosure at all is made of the use of either an 80/20 spine/resin graft latex or the ability to carry out the polymerization using suspension techniques.
U.S. Pat. No. 3,637,555 merely discloses new stabilizer systems for ABS, but in the disclosure there is cross-reference to a co-pending application, Ser. No. 748,656, involving the use of an 80/20 spine/resin graft latex in a latex-suspension process. Counterparts of this co-pending application have been issued in Canada (877,378), Britain (1,253,242) and France (2,014,012).
In British Patent No. 1,253,242 a latex-suspension process somewhat similar to the present latex-suspension process is disclosed. The process involves addition of monomers and a graft latex to a suspending solution. However, no reference is made to using a spine latex in the process, nor is any mention made of the enhancement of the properties of the product by using a specific particle size.
In British Patent No. 1,315,513 the latex-suspension process is the same as described in British Patent No. 1,253,242 except that the monomer system is styrene and methyl methacrylate.
Japanese patent publication 47/47864 describes a process wherein styrene/acrylonitrile monomers are bulk polymerized to 1-45% monomer conversion, after which a spine or a graft latex is added to the bulk polymerized monomers and the mixture is suspended, followed by the addition of a second portion of spine or graft latex and finally, by polymerization of the entire mass to form beads. If the bulk polymerization step is run to 1% conversion and the latex added after the addition of the suspending solution, the final process is almost identical to the process described in British Patent No. 1,253,242.
French Patent No. 2,148,171 describes a process similar to British Patent No. 1,253,242 except for the use of spine latex in place of graft latex.
U.S. Pat. No. 3,370,105 describes a latex-suspension process which involves addition of spine latex to monomers, complete coagulation of the latex and vigorous agitation to obtain the desired particle size in the suspension stage. Polymerization is initiated after coagulation in this process.
In Japanese patent publication 48/05870 there is described a latex suspension process which involves adding a spine latex to the monomers and coagulatiing the mixture in the presence of an acid followed by the addition of base and suspending solution.
British Patent No. 1,356,926 describes a suspension polymerization process wherein an additive such as phosphoric acid is added to the polymerization mass to coagulate, or destroy the stability of the rubber latex after which the suspension is polymerized.
Finally, it is known, from U.S. Pat. Nos. 3,793,403 and 3,573,243 that SPS spine may be agglomerated either chemically or by pressure. The agglomerated spine is thereafter used in standard emulsion polymerizations, but not in latex suspension processes.
The preparation of tough, impact resistant plastics by the grafting of resin-forming monomers onto elastomeric spines is well known. Examples of such materials which are prepared commercially are high impact polystyrene and ABS polymers. The latter materials, for example, are graft copolymers of styrene and acrylonitrile on butadiene elastomers such as SBR (styrene-butadiene rubber) or polybutadiene. More precisely, the ABS polymers are comprised of (1) a continuous phase consisting essentially of styrene acrylonitrile copolymer, and (2) a disperse phase consisting essentially of butadiene (or SBR) elastomer uniformly dispersed throughout the continuous phase. The graft copolymer provides cohesiveness to the system by overcoming the incompatibility of the resin and the elastomer with each other.
ABS polymers have been prepared for many years by carrying out the polymerization by an aqueous emulsion process (U.S. Pat. Nos. 2,802,808; 2,820,773 and 2,994,683). The rubber latex is thereby grafted with styrene and acrylonitrile with the simultaneous in situ, formation of ungrafted styrene-acrylonitrile copolymer.
Adjustment to the desired rubber level for specific properties is made either in the initial recipe or by the addition of varying amounts of free styrene-acrylonitrile emulsion latex. The resulting latex is then flocced, dried and compounded.